SARG: the high resolution spectrograph

Abstract

SARG is the high resolution spectrograph of TNG. It has been in operation since late spring 2000. SARG is a cross dispersed echelle spectrograph; it offers both single object and long slit (up to 26 arcsec) observing modes covering a spectral range from {\lambda}=0.37 up to 1 {\mu}m, with resolution ranging from R=29,000 up to R=164,000. Cross dispersion is provided by means of a selection of four grisms; interference filters may be used for the long slit mode (up to 26 arcsec). A dioptric camera images the cross dispersed spectra onto a mosaic of two 2048x4096 EEV CCDs (pixel size: 13.5 {\mu}m) allowing complete spectral coverage at all resolving power for {\AA} <0.8 {\mu}m. An iodine-absorbing cell allows to obtain high precision radial velocities. A Distributed Active Temperature Control System (DATCS) maintains constant the temperature of all spectrograph components at a preset value. Early results show that SARG works according to original specifications in terms of wavelength coverage, efficiency (measured peak efficiency is about 13%), resolution (maximum resolution R~164,000 using a 0.3 arcsec slit, R~144,000 using an image slicer), and stability (preliminary estimates of the radial velocity accuracy is ~5 m/s using the iodine cell and ~ 150 m/s without the cell).